1.Field of the Invention
This invention relates to an optical information processing method and apparatus for scanning an optical recording medium provided with tracks by a light beam and for effecting recording and/or reproduction of information while effecting tracking servo of the light beam.
2. Related Background Art
Various examples such as a disc-like form, a card-like form and a tape-like form are known as the forms of information recording media for recording information thereon and for reading out the information recorded thereon. Also, recently, attention has been paid to a method of applying a light beam condensed in the form of a spot to such media to thereby accomplish recording and reading-out of information, because of its capability of enhancing the recording density.
The manner of such recording will hereinafter be described by taking as an example a case wherein use is made of a card-like optical recording medium (hereinafter referred to as an optical card).
FIG. 1 of the accompanying drawings is a schematic plan view of the optical card, and FIG. 2 of the accompanying drawings is a fragmentary enlarged view thereof.
In FIG. 1, the letter C designates the optical card, the reference numeral 72 denotes information tracks, and the reference numeral 73 indicates the home position. Information is recorded as optically detectable record pit rows (information tracks) on the optical card C by causing a light beam modulated in accordance with recording information and reduced down into a minute spot to scan the card C. At this time, to record or reproduce information accurately without causing any trouble such as crossing of the information tracks 72, it is necessary to control the applied position of the light beam in a direction perpendicular to the scanning direction (auto tracking, hereinafter referred to as AT). Also, to apply the minute spot stably in spite of any bending or mechanical error of the optical card, it is necessary to control the applied position of the light beam in a direction perpendicular to the optical card (auto focusing, hereinafter referred to as AF). As shown in FIG. 2, tracking tracks 75 (75.sub.1, 75.sub.2, . . . ) for effecting the aforementioned AT are provided between the information tracks 72 (72.sub.1, 72.sub.2, . . . ) of the optical card C.
A method of recording information on the optical card will now be described.
In FIG. 1, the light beam is at first positioned at the home position 73. The light beam is then moved in the direction of arrow D to seek an information track 72.sub.n to be recorded, and scans the information track 72.sub.n in the direction of arrow F, thereby accomplishing recording or reproduction of information. Track numbers are recorded on the information tracks 72, and by reproducing this information, the information track currently being recorded can be determined. Also, recording of information is carried out in the fashion of a postscript, i.e., in the order of the information tracks 72.sub.1, 72.sub.2, . . . , 72.sub.n.
FIG. 3 of the accompanying drawings is a block diagram showing the construction of an information recording-reproducing apparatus for the optical card as described above.
In FIG. 3, a system controller 28 controls motors 26 and 27 and AT and AF servo circuits 24 and 25 to thereby control recording or reproduction of information on the optical card C.
The motor 26 reciprocally moves the optical card C in the direction of double-head arrow a, whereby a light beam is applied from an optical head 23 along the information tracks of the optical card C. The motor 27 is for moving the optical head 23 in a direction perpendicular to the information tracks on the optical card C.
The optical head 23 includes a light source 23a comprising a semiconductor laser, a collimator lens 23b for collimating the light beam from the light source 23a, a beam splitter 23c and an objective lens 23d, and applies a light beam for recording/reproduction onto the recording surface of the optical card C.
The optical head 23 also includes a beam splitter 23e, condensing lenses 23f and 23g, and photoelectric converters 23h and 23i. The light beam reflected on the recording surface of the optical card C is received by the photoelectric converters 23h and is 23i and converted into electrical signals thereby, and the electrical signals are supplied to the AT servo circuit 24 and the AF servo circuit 25, respectively.
The AT servo circuit 24 and the AF servo circuit 25 direct driving currents to the tracking actuator 23j and focusing actuator 23k of the optical head 23 to thereby move the objective lens 23d and to effect AT and AF control.
The basic construction of such an information recording-reproducing apparatus is disclosed, for example, in U.S. Pat. No. 4,912,697 and in U.S. Pat. No. 5,010,534.
FIG. 4 of the accompanying drawings shows an example of the prior art relating to the circuits around the above-described AT servo circuit.
The reference numeral 1 designates a photo-detector for converting laser light subjected to reflection and modulation on a recording information carrier into electric current, the reference numeral 2 denotes a preamplifier for extracting an information signal HF and a focusing error signal FE by the output of the photodetector 1, the reference numeral 3 designates a tracking error amplifier for extracting a tracking error (AT error) signal from the output of the photodetector 1, the reference numeral 4 denotes a tracking drive circuit for converting the tracking error signal into a control signal for stably driving a tracking actuator 6, the reference numeral 5 designates an amplifier, the reference numeral 7 denotes a change-over switch for changing over the tracking error signal and the output signal 21 of an oscillator 16 by a control signal 19 from a servo controller 15, the reference numeral 17 designates a comparator, the reference numeral 32 denotes an AND gate, and the reference numeral 33 designates a D flip-flop circuit.
In the construction as described above, the laser light subjected to reflection and modulation on the information recording carrier includes the recording information and information regarding focusing error and tracking error, and this laser light is photoelectrically converted by the photodetector 1, and a recording information signal and a focusing error signal are extracted by the preamplifier 2.
On the other hand, the tracking error signal is extracted by the tracking amplifier 3. In the ordinary reproduction mode, the switch 7 is connected to the tracking servo amplifier 3 side. Accordingly, the tracking error signal is sent to the tracking drive circuit 4 and drives the tracking actuator 6, whereby AT is effected.
The following process has heretofore been utilized to cause a shift from the auto tracking-OFF state to the auto tracking-ON state as described above.
The controller 15 sends an oscillation permission signal 20 to the oscillator 16. At the same time, the controller 15 supplies a control signal 19 for connecting the change-over switch 7 to the output side of the oscillator 16. The oscillator 16 outputs a triangular wave to thereby reciprocally move the tracking actuator at a predetermined amplitude and a predetermined speed in a direction across the tracks through the tracking drive circuit 4. At that time, any change in the AT error signal is input to a comparator 17.sub.1, and whether the AT error signal has reached a value V.sub.1 preset by a voltage varying device 18.sub.1 is monitored. If the AT error signal exceeds the value V.sub.1, the comparator 17.sub.1 inputs a high level signal to the D flip-flop 33. Even after the AT error signal becomes below the value V.sub.1, the D flip-flop 33 continues to output a high level signal to the AND gate 32. On the other hand, the AT error signal is input to a comparator 17.sub.2, and whether this signal is below a value V.sub.2 preset by a voltage varying device 18.sub.2 is monitored. The comparator 17.sub.2 outputs a high level signal to the AND gate 32 during a period of time when the AT error signal is below the value V.sub.2. That is, the output of the AND gate 32 does not assume a high level until the AT error signal first exceeds the value V.sub.1 and then decreases below the value V.sub.2. When this high level signal is input, the controller 15 sends a change-over signal to the switch 7 to thereby connect the tracking drive circuit 4 to the tracking amplifier 3 and to operate the tracking servo.
FIGS. 5 and 6 of the accompanying drawings illustrate a light beam spot as it relatively crosses the tracks on the recording carrier in the aforedescribed auto tracking-OFF state. FIG. 5 schematically shows the relative positional relation of information tracks 72.sub.n-1 and 72.sub.n and tracking tracks 73.sub.n-1 -73.sub.n+1 with this light beam spot, and in the figure, reference characters a-h show the manner in which that positional relation changes every moment. FIG. 6 is a signal waveform graph showing the detection signals of beam spots E and F corresponding to the states a-h and the AT error signal (E-F).
Here, the beam spots E and F are detected by the reflected lights thereof being received by a photoelectric conversion element 23h shown in FIG. 4.
Description will now be made of the process until a shift is made by the circuit shown in FIG. 4 from the auto tracking-OFF state to the ON state in which tracking servo has been applied. FIGS. 7 and 8 of the accompanying drawings show the circumstances during this process. In the example shown in FIG. 7, when the beam spot moves relatively upward in the plane of the drawing sheet, the detection signals of the beams E and F and the AT error signal exhibit the waveforms as shown in FIG. 8. Here, when the AT error signal becomes lower than a voltage V.sub.2 in the vicinity of OV after the AT error signal becomes greater than a predetermined voltage V.sub.1, the servo loop is closed. Accordingly, from and this point and as shown in FIG. 7, the light spot traces the information track 72n. The predetermined voltage V.sub.1 is determined by the contrast of the information tracks 72.sub.n, 72.sub.n-1 and the tracking tracks 73.sub.n-1 -73.sub.n+1.
However, in the above-described example of the prior art, if as in the example shown in FIG. 9 of the accompanying drawings, there is on the information recording carrier a defect D whose reflectivity is lower than or of the same degree as that of the tracking tracks, the AT error signal when the spot E or F crosses the defect D becomes greater than the predetermined value V.sub.1 as shown in FIG. 10 of the accompanying drawings. The comparator 17 outputs an inversion signal to the AND gate 32. Therefore, the controller 15 tries to close the AT servo loop immediately after the state a'. Actually, however, the spots E and F are not entering the tracking track and therefore, as shown in FIG. 10, AT failure (out of AT) occurs. The influence of such a defect poses a problem not only when the tracking-ON state is entered from the tracking-OFF state at the start of the operation of the apparatus, but also when track jump is effected. The track jump refers to the operation of temporarily switching off the tracking from the state of tracking operation servo and moving the light spot to another track and again restoring the tracking-ON state.